Weed control and root barrier

ABSTRACT

A weed control root barrier includes a polymeric sheet material having spaced apart nodules or disks comprising a polymer containing a herbicide. The sheet is porous to permit free passage of water. It may be a non-woven fabric of non-biodegradable polyolefin material. Diffusion of the herbicide directly into the soil is controlled by a barrier material coated on selected portions of the nodules or disks. In one embodiment, essentially all the herbicide in the nodules or disks is directed into the soil via long term migration through and away from the sheet. The barrier layer is coated on portions of the nodules or disks facing the back surface of the carrier to block release of the herbicide to areas of the soil where it is not needed. Exposed surface portions of the nodules can be coated with the barrier material, leaving uncoated sides of the nodules from which herbicide may be released into the soil along a narrow zone of protection generally parallel to the front face of the carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/099,645, filed May 3, 2011, and claims priority to U.S.Provisional application 61/731,713, filed Nov. 30, 2012. The contents ofboth applications are fully incorporated herein by this reference.

FIELD OF THE INVENTION

This invention relates generally to products used for root barriersand/or weed control; and more particularly, to flexible sheet materialsthat function as carriers for spaced apart layers of rootgrowth-inhibiting material attached to and distributed across the faceof the sheet material. These products, when placed in the ground, slowlyrelease the root growth-inhibiting material at a release rate thatprovides continuous long term protection against undesired root growth.

This application is a continuation-in-part of my pending U.S.application Ser. No. 13/099,645, filed May 3, 2011. This applicationalso claims priority to my U.S. Provisional Application No. 14/350,801,filed Nov. 30, 2012. Both applications are incorporated herein, in theirentirety, by this reference.

BACKGROUND

Original work done by Battelle (Battelle Memorial Institute) in the1970s was directed to keeping root growth out of nuclear waste burialsites for a minimum expected life of 100 years. Battelle addressed theproblem by developing buried pellets containing a herbicide(2,6-dinitroaniline) incorporated into a polymer (polyethylene) alongwith carbon black. The Battelle buried pellets, approximately 9 mm indiameter, were placed directly into the soil on a grid pattern at 2.5 to5.0 cm spacing.

The work done by Battelle later resulted in issuance of U.S. Pat. Nos.5,116,414 and 5,181,952 to Burton et al. Both of these patents discloseporous sheet materials having spaced apart bodies of a polymercontaining 2, 6 dinitroaniline for use as a root growth-inhibitingproduct; and both patents are incorporated in their entirety herein bythis reference.

In the 1980s, Battelle's idea was followed by a development ofgeotextiles, particularly a non-woven fabric used as a carrier forpellets containing a herbicide. Pellets containing the herbicidetrifluralin are spaced apart across the surface of the fabric, and whenthe fabric is buried in the ground, it affords protection againstundesired root growth. One development which has been in use for manyyears is the geotextile fabric supplied by Fiberweb, Inc. which includesa pattern of nodules containing the herbicide trifluralin. That rootbarrier and weed control product is and has been sold under theregistered mark Biobarrier, and is referred to herein as “the Biobarrierproduct.”

In the Biobarrier product, the presence of the trifluralin prevents roottip cell division; and when the Biobarrier material is used as a rootbarrier or for weed control, for example, the root systems of the weedsdo not grow in adjacent areas into which the herbicide is dispersed.

In the Biobarrier product the nodules containing trifluralin applied tothe fabric generally have a hemispherical shape, from which theherbicide can radiate directly outward into the soil during use. In oneembodiment, the nodules have a radial dimension of about 9 mm, with amutual spacing of about 4 cm. Each nodule radiates out a protectivespherical dimension of about 3 mm, so each protects a sphere volume ofabout 14 cu cm. Assuming an area of 1 sq m, with nodules at 4 cmspacing, there are 625 nodules/sq m, or a zone of protection of 8,750 cucm formed by the trifluralin moving in overlapping spheres directly awayfrom the nodules.

The present invention is based on a recognition that the amount ofherbicide used in the Biobarrier product, or similar products, isexcessive, in fact wasted, given the amount of herbicide actually neededto provide a practical level of protection. This invention provides amuch more efficient use of the herbicide material. Assuming the same 1sq. m area of the fabric, for instance, effective narrow zones ofprotection having a volume of 1,000 cu cm or less can be produced alongthe fabric by the present invention. This saves the amount of herbicidebeing used and thereby avoids the otherwise undesired wasteful prior artuse of the herbicide. Advantages of the present invention include longerlife of the herbicide and/or lower product cost for the same level ofprotection. Other improvements are also provided, as described in moredetail below.

SUMMARY OF THE INVENTION

Briefly, one embodiment of the present invention comprises a materialfor preventing entry of unwanted roots into a volume of soil. A flexiblecarrier sheet of a porous herbicide-absorbing material, such as apolyolefin material, includes discrete spaced-apart layered segments ofa polymer containing a herbicide, such as a herbicidal dinitroaniline ina composition effective to retain and control the release rate of thedinitroaniline. The layered segments can contain a dispersed nanoclay tofurther control release rate.

In one embodiment of the invention, the layered segments can include apolymeric barrier film applied to selected exposed surfaces of thelayered segments. The barrier material blocks diffusion of the herbicidethrough the surfaces of the layered segments covered by the barrierfilm. When the carrier sheet material is buried in soil, the areascovered by the barrier prevent diffusion of the herbicide directly fromthose areas of the layered segments into the soil. The surfaces of thelayered segments, being covered by the barrier material, can cause theherbicide to diffuse into the carrier sheet away the layered segments,and from there into the adjacent soil at such a rate, and over such aperiod of time, as to exclude roots over a period of years withoutkilling plants beyond the seedling stage.

In one embodiment, the barrier layers can prevent direct movement of theherbicide out of the layered segments and into the soil, which forcesessentially all of the herbicide contained in the layered segments to bedirected laterally through the carrier sheet and dispersed therefrom ata controlled release rate. As a result, the long term effectiveness ofthe product can be increased greatly at a substantial cost savings.

In another embodiment of the invention, the barrier material is coatedon a back surface of the layered segments, opposite from the side of thecarrier sheet that faces the root growth. The barrier prevents theherbicide from migrating away from the back surface of the carrier sheetwhere it would be of no use. In this embodiment layered segments on thefront surface of the carrier can be uncoated to allow a combination ofdiffusion into a narrow zone of protection in the soil—directly from thelayered segments and directly from the exposed front surface of thecarrier sheet.

In a further embodiment, the layered segments can have a narrow profilealong the front surface of the carrier sheet, on the side that faces theroot growth. In this instance, a front surface portion of the layeredsegments can be coated with the barrier material, leaving side portionsof the segments uncoated and facing in a direction generally parallel tothe front surface of the carrier sheet. The back sides of the layeredsegments, on the back surface of the carrier, are coated with thebarrier material to prevent the herbicide from migrating into the soilfrom the back sides of the layered segments. This embodiment forms acombined narrow zone of protection along the front side of the carrier.The herbicide is directed into the soil from the uncoated sides of thelayered segments, generally parallel to the front face of the carrier.The barrier portions of the layered segments block and thereforeminimize inefficient use of the herbicide beyond the narrow zone ofprotection. The herbicide is also directed away from the layeredsegments and laterally into the carrier, and then directly into the soilalong the exposed front surface of the carrier.

These and other aspects of the invention will be more fully understoodby referring to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a semi-schematic illustration of a prior art geotextile sheetmaterial containing spaced-apart nodules of a root growth-inhibitingmaterial.

FIG. 2 is a cross-section taken on line 2-2 of FIG. 1 and depictingdimensions of the nodules characteristic of the prior art sheetmaterial.

FIG. 3 is a semi-schematic illustration showing a geotextile sheetmaterial with spaced apart layered segments having barrier propertiesaccording to principles of this invention.

FIG. 4 is a cross-section taken on line 4-4 of FIG. 3 and depictingdimensions of the layered segments according to the present invention.

In the accompanying drawings, FIGS. 5 through 10, the roots are depictedas approaching from the right hand side. The arc of dots marked “a”symbolizes the movement of the herbicide away from the layered segments,nodules or disks. The flat plane of dots marked “b” symbolizes movementof the herbicide away from the fabric.

FIG. 5 shows a prior art product. The original fabric is typicallywhite, but the herbicide has migrated from the pellets carried by thefabric through the fabric, approximately equally on both sides, todiscolor the fabric.

FIG. 6 shows a schematic cross-section of the prior art product with thedots symbolizing the movement of herbicide through the soil. The largecircle of dots marked “a” symbolizes the movement of the herbicide awayfrom the nodules contained in the prior art product.

FIG. 7 shows a schematic cross-section with a barrier molded on the backof a nodule. The dots symbolize the movement of herbicide through thesoil, with the only movement on the protected side being movement fromthe fabric.

FIG. 8 shows a schematic cross-section with a barrier molded on bothsides of the nodule. The dots symbolize the movement of herbicidethrough the soil, with the only movement on both sides being movementfrom the fabric.

FIG. 9 shows a disk-shaped layered segment molded to a non-porousplastic sheet with a barrier molded over the top of the disk. The sheethas a barrier layer so that no herbicide moves out from the rear side ofthe sheet.

FIG. 10 shows a disk-shaped layered segment molded through the fabricwith a barrier applied to both sides of the disk.

FIG. 11 is a schematic cross-sectional plan view illustrating anexperimental root growth-intrusion comparison between a prior art weedcontrol and root barrier product and an improved product made accordingits principles of this invention.

FIG. 12 is a schematic cross-sectional side view taken on line 12-12 ofFIG. 11.

FIG. 13 is a schematic diagram illustrating a sheet of a root growthbarrier fabric used in the comparative tests.

FIG. 14 is a cross-sectional view illustrating a co-extruded form of thelayered segments of herbicide-containing material and their resinousbarrier layers, according to one method for making the product of thisinvention.

FIG. 15 is a schematic plan elevational view showing a pattern ofco-extrusions produced by a co-extruder used in the process of FIG. 14.

FIG. 16 is a fragmentary plan elevational view showing a finishedgeotextile fabric with the co-extruded pattern formed by the co-extruderof FIG. 15.

FIG. 17 is a cross-sectional view taken on line 17-17 of FIG. 16.

FIG. 18 is a cross-sectional view illustrating a co-extruded form of thelayered segments of herbicide-containing material and their resinousbarrier layers, according to another method for making an alternateembodiment of the invention.

FIG. 19 is a schematic plan view showing a pattern of co-extrusionsproduced by a co-extruder used in the process of FIG. 18.

FIG. 20 is a fragmentary plan elevational view showing a non-porousfabric with a pattern of co-extrusions formed by the co-extruder of FIG.19.

FIG. 21 is a cross-sectional view taken on line 21-21 of FIG. 20.

FIG. 22 is a fragmentary schematic diagram (not to scale) showing across-sectional illustration of an alternate embodiment of the inventionthat blocks migration of herbicide away from a root growth area, on abackside of the sheet material.

FIG. 23 is a fragmentary schematic diagram (not to scale) showing across-sectional illustration of a further alternate embodiment of theinvention which produces a narrow zone of protection along a side of thesheet material that faces a root growth area.

DETAILED DESCRIPTION

The invention is best understood by first referring to FIGS. 1 and 2,which illustrate a prior art root growth-inhibiting sheet 20. The sheetcomprises a porous non-woven polyolefin geotextile fabric 22, withnodules 24 of a polyolefin molded both into and onto the fabric. Thenodules are dispersed across the face of the sheet, preferably in auniform rectangular or square grid pattern as shown in FIG. 1. Thenodules 24 contain the herbicide trifluralin and carbon black dispersedin the polyolefin material. This product is sold under the registeredmark Biobarrier. In use, the trifluralin is released directly from thenodules into the soil. The trifluralin is also absorbed by thepolyolefin fabric and migrates through the fabric and then into thesoil, away from the free surface areas of the fabric between thenodules.

FIG. 2 depicts the size and shape of the nodules of herbicide-containingmaterial as applied to the prior art sheet 20. In the process ofapplying the nodules to the geotextile fabric sheet, the nodules areformed by molding techniques, and the hot molten material forming thenodules passes through the fabric and bonds the nodules to the sheet.The resulting nodules are formed in a generally hemispherical shape at26 on one side of the sheet and in a smaller size at 28 on the reverseside of the sheet.

Measurement tests carried out on the prior art product shown in FIGS. 1and 2 exhibited the following dimensions:

(1) In a 204 sq. inch (17-inch×12-inch) area, there are 88 of thespherical shaped nodules or approximately 62 per sq. ft., with ahorizontal and vertical spacing at about 1.2 inches between nodules.

(2) The fabric layer has a thickness of about 0.019-inch.

(3) The vertical height (V) of the nodules is about 0.31-inch, theheight of the spherical shaped nodule (H) above the sheet is 0.21 inch,and its width (w) is 0.41-inch. Each nodule's volume is 0.0333 cu inch.

FIGS. 3 and 4 illustrate a weed control and root barrier sheet 30according to principles of this invention. The sheet 30 comprises athin, flexible, non-biodegradable carrier 32 which can comprise a porousnon-woven polyolefin geotextile fabric similar to that describedpreviously; or the carrier can comprise a thin, flexible plainnon-porous sheet made of a non-biodegradable plastic material, such as apolyolefin, as described below.

Referring to the embodiment shown in FIG. 3, a pattern of mutuallyspaced-apart layered segments 34 of a herbicide-containing material areattached to a surface of the carrier sheet. The layered segments 34 areuniformly spaced-apart horizontally and vertically across the face ofthe sheet, in a pattern which can be a uniform grid pattern, or apattern with offset rows as shown in FIG. 3. The surface area of thesegments 34 is substantially larger than the projected surface areas ofthe nodules 24 in the prior art FIG. 1 embodiment. The segments 34 arealso substantially thinner, and the individual number of segments 34 perrow is reduced considerably, compared to the prior art embodiment ofFIG. 1.

The layered segments of herbicide material are attached to the carriersheet in the form of generally flat disks 36 shown in FIG. 4. Thedisk-shaped elements are generally wider in diameter or width comparedto their thickness. They are preferably applied to the carrier inflexible sheet form, by injection molding, extrusion, coating, orprinting techniques. In the process of applying the segments, the hotmolding or coating material passes through a porous carrier and can forma disk-shaped layer or film on both sides of the carrier, as well asbeing embedded in the carrier, as illustrated in FIG. 4. The process ofapplying the disk-shaped elements can vary, to produce segments whichare permanently bonded to, coated on, or otherwise embedded in thecarrier material. The embodiment of FIG. 3 shows the disk-shapedelements applied in a generally circular shape, although the shapes andpatterns of the disks or other layered segments can vary, depending upondesired molding, extrusion, coating, or printing techniques.

Following the step of applying the layered segments to the carriersheet, the exposed surfaces of the disk-shaped elements 36 or otherlayered segments are covered with a thin barrier film 38 as illustratedin FIG. 4. The exposed surfaces of the disk-shaped elements on bothsides of the carrier sheet are covered by the barrier film. The barrierfilm, described in more detail below, can be applied to the disks byinjection molding, extrusion, coating, printing, or paint coatingtechniques. The barrier film also can be applied simultaneously with themolding of the disks by means of co-injection molding. The objective isto cover virtually the entire exposed surfaces of the disks, to providea barrier between direct exposure of the herbicide-containing disks orother layered segments, and the soil, during use.

The present invention can be carried out using other shapes and sizes ofthe herbicide-containing material. For instance, in one embodiment,nodules similar to the Biobarrier product could be used, along with thebarrier layer of this invention. For reasons explained below, thebarrier layers enable one to use layered segments of various shapes andsizes, but with a reduced volume that uses much less herbicide.

Measurement tests carried out on the embodiments of FIGS. 3 and 4 havethe following dimensions:

(1) In a 204 sq. inch area, there are 16 of the disk-shaped elements, ina pattern that contains from about 11 to about 12 disks per sq. ft,compared to the FIG. 1 embodiment which contains about 64 nodules persq. ft.

(2) The fabric layer has a thickness of about 0.019 inch.

(3) The disk has a diameter of 1.0 inch and a width of 0.038 inch andhas a volume of 0.030 cu inch.

Comparatively speaking, the nodules 24 of the prior art sheet materialhave a greater volume-to-area ratio (more than 10 times greater) thanthe disk-shaped segments 34 of the present invention. In one embodimentof the invention, the volume-to-area ratio is less than 0.10 inch. (Thevolume-to-area ratio is the ratio of the volume of material contained ineach layered segment or nodule versus the surface area of the fabriccovered by the same segment or nodule. This ratio can be expressed in cucm/sq cm, for example, and can be measured in terms of an average ratiofor a specific area of the fabric.)

Referring more specifically to the present invention, the carrier sheet32, in a preferred embodiment, comprises a thin, flexible porouspolymeric carrier material, and more particularly, a non-wovengeotextile fabric material described previously. The preferredcomposition of the carrier sheet is a polymeric material to which thelayered segments can be bonded or embedded and which can absorb theherbicide that diffuses or migrates from contact with the layeredsegments. A presently preferred carrier material is a thermoplasticpolyolefin such as polyethylene or polypropylene made into the non-wovenfabric. The present invention is based in part on a recognition thatsuch carrier materials absorb the diffused herbicide similar to a spongeor ink blotter, constantly absorbing the herbicide migrating from thelayered disk elements into the carrier, and transmitting the absorbedherbicide laterally through the carrier, from which the herbicide isreleased into the soil at a desired continuous and controlled releaserate.

In addition to thermoplastic polyolefin materials generally, the carriersheet more specifically can be made from the group of materialsconsisting of polyethylenes, polypropylenes, copolymers and mixtures ofpolyethylenes and polypropylenes, polyvinylacetate, poly(ethylene vinylacetate), poly(ethyleneacrylic acid), poly(ethylene ethyl acrylate),polybutylene.

In an alternate form of the invention, if transmission of water throughthe sheet is not required, the carrier sheet can comprise a plainnon-porous non-biodegradable plastic sheet; and in one embodiment, theplastic sheet can be made from the previously described carrier sheetmaterials. The non-porous plastic sheet also can be coated with abarrier material (described below) on one side to block passage ofherbicide from that side of the sheet.

The layered segments of herbicide-containing material can comprise anypolymeric material in which the herbicide can be dispersed, which can bebonded to the carrier sheet, and from which the herbicide can migrate ata controlled rate. The herbicide material is preferably dispersed in apolymeric carrier material, preferably a thermoplastic polyolefinmaterial, such as polyethylene. More specifically, the polymer containedin the layered segments is selected from the group consisting ofpolyethylenes, polypropylenes, copolymers and mixtures of polyethylenesand polypropylenes, polyvinylacetate, poly(ethylene vinyl acetate),poly(ethyleneacrylic acid), poly(ethylene ethyl acrylate), polybutylene.

The presently preferred herbicide material is a dinitroaniline. Thecommon names and chemical identification of representativedinitroaniline compounds which can be used in the present invention are:

-   -   Trifluralin—N,N-di-n-propyl-4-trifluoromethyl        2,6-dinitroaniline, having the generic name        trifluralin-2,6-dinitro-N,N-dipropyl-p-toluidine,    -   Benfluralin—N-butyl-N-ethyl-2,6-dinitro-4(trifluoromethyl)        benzenamine,    -   Isopropalin—4-isopropyl-2,6-dinitro-N,N-dipropylaniline,    -   Oryzalin—3,5-dinitro-N.sup.4,N.sup.4-dipropylsulfanilamide,    -   Ethalfluralin—N-ethyl-.alpha.,.alpha.,.alpha.-trifluoro-N-(methylallyl)-2,6-dinitro-p-toluidine,    -   Pendimethalin—N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine,    -   Profluralin—N-(cyclopropylmethyl)-.alpha.,.alpha.,.alpha.-trifluoro-2,6-di        nitro-N-propyl-p-toluidine.

In one embodiment of the invention, the formulation for theherbicide-containing material comprises a herbicide dispersed in aparticulate material that absorbs the herbicide, such as carbon black ora nanoclay, for example. The herbicide-containing material is preferablymade by a mixture of thermoplastic polyolefin, such as polyethylene, anda herbicide absorbed into carbon black and then dispersed into thepolymeric carrier material. The amount of carbon black or otherparticulate herbicide-absorbing material in the formulation issufficient to retain and control the release rate of the herbicide. Inone embodiment, the herbicide-containing material comprises a polyolefinmaterial containing a dispersed herbicidal dinitroaniline and carbonblack in which the concentration of the herbicide is from about 2 wt. %to about 30 wt. %, based on the total solids contained in theherbicide-containing material. In another embodiment, theherbicide-containing material comprises 50% polyethylene, 25%trifluralin, and 25% carbon black. This herbicide-containing material isavailable under the mark ROOTGUARD® from Geoflow, Inc.

In one form of the invention, the herbicide-containing material caninclude a fine particulate filler material dispersed in an amount thatreduces the diffusion rate of the herbicide from the polymer at acontrolled, slow release rate. Such a fine particulate material caninclude a dispersion of a nanoclay; and more particularly, the slowrelease herbicide-containing material can be made by formulations andmethods disclosed in U.S. Pat. No. 6,821,928 to Ruskin, which isincorporated herein by this reference.

The barrier material comprises any polymeric material which can beapplied to the layered segments in thin-film form and which resists longterm migration of the herbicide through the barrier, in the sense thatmigration of the herbicide is not slowed down, but virtually stopped. Inuse, the barrier will encompass the layered segments and essentiallyblock diffusion of the herbicide directly into the soil from thedisk-shaped elements which would otherwise be in direct contact with thesoil. The barrier film causes essentially all of the herbicide from thelayered segments to be absorbed into the carrier sheet, from which theherbicide can then be released at a controlled rate from areas of thesheet not covered by the layered segments of herbicide-containingmaterial.

In one embodiment, the preferred barrier material is ethylene-vinylalcohol random copolymer (EVOH), which can be applied as a paintcoating, although any polymer that forms an impenetrable coating in drythin-film form can be used. Polymers such as those used in forming paintfilm binders, or lacquers, including vinyls, polyolefins, polyurethanes,and acrylics, are examples. In another embodiment the barrier film cancontain dispersed particles of a fine particulate filler material, suchas a nanoclay, or other nano-particles. These compositions can producebarrier films that further resist or block diffusion of the herbicidethrough the applied barrier layers.

The present invention is adapted for various uses involving inhibitionof root growth, particularly the exclusion of the roots from areas inwhich they are undesirable, e.g., waste burial sites, from undergroundpipelines, basements, hardscapes such as sidewalks, septic drain-fields,or simply the boundaries between adjacent properties. One use, inparticular, can provide a root barrier to redirect roots in onsitesewage drain fields. As mentioned previously, the herbicide-containinglayers may be formed of polymers, e.g., polyethylene, containing inadmixture dinitroanilines, such as N,N-di-n-propyl-4-trifluoromethyl2,6-dinitroaniline, having the generic name trifluralin. Referring tothe prior art, during use the Biobarrier product releases trifluralindirectly from the nodules into the soil. The trifluralin also isabsorbed by the polyolefin fabric and moves through the fabric into thesoil. Inhibiting movement of the trifluralin directly into the soil fromthe nodule (as with the present invention) can increase considerably theeffective life of the product. EVOH and nanoclay compounds, for example,are effective barriers to the movement of dinitroanilines. This isachieved by the present invention when the barrier layers are placedimmediately between the layered segments and the soil. The Biobarriermaterial releases trifluralin directly into the soil on both sides ofthe fabric. The trifluralin moves in overlapping spheres away from eachnodule, which is unnecessary and wasteful, as described previously. Withthe present invention, narrow zones of protection can be provided alongboth sides of the non-woven fabric while efficiently using much less ofthe trifluralin. The root barrier is typically required in only onedirection. The non-woven fabric is used when water passing through ineither or both directions is required. If permeability of air and wateris not required, a solid plastic sheet (such as that describedpreviously) with a barrier layer of EVOH or a nanoclay-containingcompound will restrict movement of the trifluralin to one direction.

In accordance with this invention, a particularly desirable embodimentis the non-woven fabric of non-biodegradable polyolefin material. Thistype of material, known as a “geotextile” can be used with thisinvention for weed control, prevention of erosion on slopes, and otherlandscaping purposes. As mentioned previously, the polymer containingthe root repellant dinitroaniline may be applied to the carrier sheet invarious forms, e.g., as buttons or disks. The choice of the specificmode of distribution depends to a large part on the life desired for theroot repellency.

The effectiveness of the invention in inhibiting root elongation iscontrolled by the soil concentration of dinitroaniline adjacent to thebarrier. This is regulated by the release rate of the dinitroanilinefrom the disk-shaped elements into the sheet and from there into thesoil. By inhibiting movement of the dinitroaniline directly into thesoil, and forcing essentially all of the herbicide contained in thelayered segments to move laterally through the carrier sheet, theinvention enables use of various shapes and sizes of the segments, toutilize a reduced amount of herbicide. The barriers thereby reduce therate of loss of herbicide from the layered segments, thereby reducingcosts and/or extending the effective life of the product.

FIGS. 5 through 10 illustrate comparative uses of the invention. FIG. 5illustrates a prior art weed control product 40, such as a prior artBiobarrier product. The herbicide-containing nodules 42 are distributedacross the face of the sheet 44.

FIG. 6 shows a cross-section of the prior art product 40. The nodules 42are structured similar to the nodules in FIG. 2. The dots marked “a”illustrate movement of the herbicide through the soil away from bothsides of the sheet. The herbicide contained in the nodules will radiateoutwardly directly into the soil as shown. The originally color of thesheet is white, but during use, the herbicide also migrates from thenodules into the sheet, and discolors the sheet, relatively uniformly,along both sides of the sheet.

FIG. 7 shows an alternate sheet material in which the prior art productof FIG. 6 has been altered by applying a barrier film 46 to the reverseside of the nodules 48 carried on the sheet 50. The barrier film issimilar to that described previously. The dots “a” symbolize movement ofthe herbicide through the soil. The barrier layers 46 block dispersionof the herbicide into the soil on the reverse side of the carrier sheet,while the herbicide radiates outward from the nodules into the soil andalso migrates through the sheet, and then into the soil.

FIG. 8 shows another alternate sheet material in which the prior artproduct of FIG. 6 has been altered by applying the barrier film 52 tothe outwardly projecting curved surfaces of the nodules 54, on the frontface of the carrier 56. The barrier is also applied to the portions ofthe nodules exposed to the reverse side of the sheet. The dots marked“a” symbolize movement of the herbicide through the soil, with the onlymovement on both sides being movement from the carrier sheet.

FIG. 9 illustrates one embodiment of the invention in which the layeredsegments 58 of herbicide-containing material according to the inventionare applied to a front face of the carrier sheet 60. The carrier sheetcomprises a non-porous plain plastic sheet comprising a polymericmaterial, such as polyolefin, which is capable of absorbing migratingherbicide from the layered segments. The barrier layers 62 are appliedto the exposed surfaces of the layered segments, to provide a barrierbetween the segments and the soil. A second barrier layer 64 is appliedto the entire reverse surface of the sheet 60. The dots “b” illustratemovement of the herbicide in a direction away from the front face of thecarrier into the soil. The carrier sheet with its barrier layer on thereverse side has no herbicide moving out from the reverse side of thesheet. Movement of herbicide away from the individual layers ofherbicide material is blocked by the barrier layers 62.

FIG. 10 shows an alternative form of the invention in which disk-shapedlayered segments 66 are molded through the carrier sheet 68 and exposedto both sides of the carrier sheet. These disk-shaped layered segmentsare covered by separate barrier layers 70 applied to both sides of eachdisk. The dots marked “b” in FIG. 10 illustrate movement of theherbicide during use, in which the barrier layers block movement of theherbicide directly outwardly from the exposed surfaces of the layeredsegments. The herbicide is absorbed by the carrier sheet and theherbicide migrates outwardly from this sheet at a control release rate.

The FIG. 9 embodiment shows the most conservative use of the herbicide,followed by the embodiment of FIG. 10. The thickness of the larger, flatlayered segments can have a nearly linear effect on the expected life ofthe patent. Use of the larger, flat segments makes it comparativelyeasier to apply the barrier layer—by rotogravure printing, for example.

For the layered segments formed as disks, spacing is generally on 1-inchto 3-inch centers, to produce a protective soil area. The dinitroanilinewill slowly diffuse from the polymer with which it is mixed at acontrolled rate. It will move through the sheet to be adsorbed to thesoil adjacent to the barrier, and thus establish a zone in which theconcentration is such as to prevent further elongation or penetration ofthe adjacent roots. As mentioned previously, the rate of diffusion fromthe button or disk into the sheet may be controlled by adding nanoclayto the composition of the button or disk as taught by U.S. Pat. No.6,821,928 to Ruskin.

Some possible configurations using this invention, when compared withthe Biobarrier prior art product, are shown below:

Biobarrier As Improved Nodule Disk Diameter 0.419 inch Diameter 1.0001.250 1.500 inch Volume 0.092 cu inch Thickness 0.025 0.040 0.040 inchArea 0.152 sq inch Volume 0.020 0.049 0.071 cu inch Spacingcenter-to-center 1.500 inch Area 0.785 1.227 1.766 sq. inch Ratio:Spacing center-to-center 2.082 2.332 2.582 inch Pellet:space 6.75%Ratio: Free Space   93% Pellet:space 18.12% 22.56% 26.50% Free Space  82%   77%   73%

Advantages of this invention are:

-   -   Longer life of the trifluralin and/or lower cost than the        presently known Biobarrier product.    -   Less obnoxious blooming of trifluralin to the surface of the        product.    -   Less environmental impact because less trifluralin is released        per unit of time.    -   The dinitroanilines, in the concentrations released by the        polymers, do not translocate into other parts of the plants.        They do not kill plants beyond the seedling stage and do not        injure them, except that growth may be restricted by the        inhibition of new root production.

The present invention also addresses problems of temperature sensitivitywith prior art weed control and root barrier products. With a barrierfabric placed vertically in a trench, the upper areas of the fabricbeing located nearer the surface can experience more heat buildup duringuse. The greater heat levels heat the trifluralin which boils off at thetop more rapidly, thereby reducing expected product life.

Alternatively, a barrier fabric placed longitudinally in a shallow depthof soil, for weed control, can experience a heat sensitivity problem andreduced product life.

In one embodiment, the present invention addresses the heat sensitivityproblem by incorporating a dispersed nanoclay into the carrier sheetfabric or material. The dispersed nanoclay reduces the release rate ofthe herbicide, such as trifluralin, at elevated temperatures, which canextend product expected life.

In another embodiment, the heat sensitivity problem can be reduced byproviding a greater distribution of the layered segments on an uppersection of the fabric, or by increasing the thickness of the layeredsegments in the areas of the fabric exposed to higher temperatures.

Example

Two plastic containers with internal dimensions of 18.5″×18.5″×15″ high,as illustrated in FIGS. 11 and 12 were set up as follows:The containers were filled with potting soil.

-   -   80 shows the container: L×W×H: 18.5″×18.5″×15″;    -   82 shows the heavy root growth;    -   84 shows a salix alba vitellina (golden willow) tree;    -   86 shows a drip irrigation line; and    -   Referring to FIG. 13, 87 shows a sheet of Biobarrier fabric        18.5″ wide and 15″ high, with nodules 88 on the right hand side.        In the experiment, six rows of six nodules on the right hand        side were removed, leaving 36 small holes in the non-woven        fabric. Two such sheets were prepared.

The Biobarrier sheet placed in one container had the remaining noduleson the left hand side of the sheet coated with an EVOH(ethyl-vinyl-alcohol) paint, as shown at 89 in FIG. 13.

The Biobarrier sheet placed in the second container was left asunchanged except for the removal of 36 nodules as described above.

A and B in FIG. 13 show specific holes through which roots intruded.

Both containers were identical except for the EVOH coating. The salixalba vitellina (golden willow) is a tree with very rapid and aggressiveroot growth. The trees grew for six months through the summer of 2010.The soil was then carefully removed. Root growth and root intrusionthrough the Biobarrier were observed. In both cases there was extremelyaggressive root growth on the side where the tree was planted. In thecase of the EVOH-treated Biobarrier, all the growth was contained behindthe barrier except for one root coming through the hole in theBiobarrier marked B on the drawing. In the case of the untreatedBiobarrier, a root was observed passing through the hole marked A, aswell as massive growth under the Biobarrier on the side where thenodules had been removed. Note that B is much farther away from thenearest nodule than A.

The non-woven fabric is white and the trifluralin is orange, so one canobserve the concentration of trifluralin by the intensity of the orangecolor. Trifluralin evaporates rapidly at elevated temperatures so onecan expect that the fabric closest to the surface will be lighter incolor than deeper down. Furthermore one could expect that the fabricfurthest from the nearest nodule would be lighter. In the case of theuncoated nodules the fabric in the region on the right hand side wasnearly white. In the case of the coated nodules the color difference onthe same side, one inch below the surface, was not noticeable.

Both these observations confirm that by nearly eliminating directmovement of trifluralin out of the nodule into the soil, the lateralmovement of the trifluralin from the nodules through the fabric hasincreased.

FIGS. 14-17 illustrate a co-extrusion process for forming the product ofthis invention. As illustrated in FIG. 14, a co-extruder forms thelayered segments by simultaneously co-extruding the herbicide-containingmaterial 90 and the resinous barrier material 92 as a stripe or a bead.

FIG. 15 illustrates the output of the co-extruder which includesmultiple extruder die holes 94 which can co-extrude the stripes 96 in anoscillating pattern. The co-extruded pattern can vary as desired ineither a continuous or a discontinuous pattern or bead. In theoscillating pattern, either the co-extruder die or the fabric supportcan be oscillated.

FIG. 16 shows a finished product 98 from the co-extruder of FIG. 15, inwhich the oscillating co-extrusions 96 are applied to a continuous sheetof porous geotextile fabric 100. The co-extruded material 90, 92 issqueezed into the fabric between rollers while hot and becomes embeddedin the fabric.

FIG. 17 is a cross-sectional view of the finished product, showing thebeads of herbicide-containing material 90 and their barrier layers 92squeezed into the fabric 100.

FIGS. 18-21 illustrate a co-extrusion process for forming anotherembodiment of this invention. As illustrated in FIG. 18, a co-extruderforms the layered segments, by simultaneously co-extruding theherbicide-containing material 102 and the resinous barrier material 104as a stripe or a bead. In this embodiment, the co-extrusion is appliedto and bonded to a continuous non-porous carrier sheet. Since thelayered segments are not absorbed into the depth of the sheet, thebarrier layer 104 of the co-extrusion shown in FIG. 18 encompasses theentire exposed outer surface of the herbicide-containing component 102of the co-extrusion.

FIG. 19 illustrates the output of the co-extruder which includesmultiple extruder die holes 104 which co-extrude the stripes 106 in anoscillating pattern. The co-extruded pattern can vary in either acontinuous or discontinuous pattern of stripes or beads.

FIG. 20 shows a finished product 108 from the co-extruder of FIG. 19, inwhich the co-extrusions 106 are applied to a surface of a continuousnon-porous carrier sheet 108 such as a sheet of polyolefin material. Theco-extrusions are laid on and bonded to the surface of the sheet 108.

FIG. 21 is a cross-sectional view of the finished product, showing thebeads of herbicide-containing material 102 and their barrier layers 104adhered to the surface of the sheet. The sheet can be in multi-layerform, with a bottom layer 110 forming a barrier to the movement of theherbicide to one side of the sheet. Alternatively, the barrier layer 110can be a continuous coating of a barrier paint.

FIG. 22 shows an alternate form of the invention that reducesinefficient use of the herbicide. In this embodiment the sheet materialis illustrated buried in soil with a front face of the carrier sheet 112facing toward a root growth area. The carrier sheet preferably comprisesthe previously described porous fabric made of a polyolefin material,typically 0.019 inch in thickness. The nodules 114 applied to the frontface of the carrier sheet are similar in composition to those describedpreviously. The nodules 114 are generally hemispherical in shape, about⅜ inch in diameter. The nodules 114 can be distributed in a pattern orarray, generally uniformly spaced apart, in a grid pattern, for example.The pattern can contain about 32 nodules per sq. ft. In addition, theFIG. 22 embodiment (which is similar to that illustrated in FIG. 7) hasa narrow layer of herbicide material 114 a formed on the back surface ofthe carrier sheet which faces away from the root growth side of thesheet material. In this embodiment the layers 116 of the previouslydescribed barrier material are coated onto the exposed outer surfaces ofthe narrow layers 114 a. The remaining portions of the carrier sheetmaterial, other than the areas where the nodules are applied, are leftuncoated. (This keeps the overall barrier porous to water movement.) Thebarrier layers 116 prevent the herbicide from migrating away from theback surface of the carrier sheet, where it would be of no use. Thearray of nodules is uncoated on the front side of the carrier sheet.This causes a combination of diffusion of herbicide into a narrow zoneof protection along the carrier sheet, both directly from the layeredsegments and directly from the exposed front surface of the carriersheet. This combination forms a generally hemispherical protected zone117 approximately 3 inches wide along the front face of the carriersheet. Because of the barrier layers 116 blocking diffusion of herbicideaway from the back side of the carrier sheet, fewer nodules can be usedper unit area when compared with the prior art FIG. 1 embodiment, forexample. (Approximately 50% reduction in material cost of the herbicidematerial is achieved.)

FIG. 23 illustrates a further embodiment of the invention which producesa narrow zone of protection along a side of the sheet material thatfaces the root growth area. The FIG. 23 embodiment is illustrated buriedin soil with a front face of the carrier sheet 118 facing toward theroot growth area. The carrier sheet preferably comprises the previouslydescribed porous fabric made of a polyolefin material, typically the0.019 inch thickness carrier sheet. The array of layered nodules 120containing the herbicide material is applied to the front face of thecarrier sheet, preferably in a uniformly spaced apart pattern, such as agrid pattern, for example. The layered nodules 120 are shown in agenerally pyramid shape having an outer circumference that tapersnarrower in a direction away from the front surface of the carrier. Asshown in the FIG. 23 cross-sectional illustration, the pyramid formsangular sides 122 that taper narrower toward a generally flattened uppersurface of the nodule. FIG. 23 also shows a narrow layer of theherbicide material at 120 a formed on the back side of the carrier sheetwhich faces away from the root growth side of the sheet material. Inthis embodiment a layer 124 of the previously described barrier materialis coated onto the exposed outer surfaces of the narrow layers 120 a.The remaining back surface of the carrier sheet is left uncoated. Thebarrier layers 124 in this region prevent the herbicide from migratingaway from the back surface of the carrier sheet where it would be of nouse, similar to the FIG. 22 embodiment.

In the FIG. 23 embodiment the flattened upper surfaces of thepyramid-shaped nodules are coated with a layer 126 of the previouslydescribed barrier material, leaving the sides 122 of the segmentsuncoated and facing in a direction generally parallel to the frontsurface of the carrier sheet. This embodiment forms a combined narrowzone of protection along the front side of the carrier. During use, theherbicide is directed into the soil from the uncoated sides of thelayered nodules, generally parallel to the front face of the carrier.The barrier portions 126 of the layered nodules block and thereforeminimize inefficient use of the herbicide beyond the narrow zone ofprotection. The herbicide is also directed away from the layeredsegments and into the adjacent carrier (as described previously) and isthen directly into the soil along the front side of the carrier.

The pyramid-shaped nodules are foreshortened when compared with themaximum vertical dimension of the uncoated hemispherical-shaped nodulesshown in FIG. 22. In the FIG. 23 embodiment the base of the pyramid isabout ⅜ inch in diameter. The volume of the nodule 120 is about the sameas the nodules 114 of FIG. 22. This form of the layered nodules 120reduces the area (or volume) of soil treated by them. The foreshortenednodules reduce the distance out beyond which the herbicide is needed,the herbicide migrating directly into the soil from the uncoated sidesof the nodules. By reducing the distance the herbicide moves through thesoil, the treated area is confined to a narrow zone of protection 127along the front side of the carrier. In the illustrated embodiment thewidth of the protected zone is about 2 to 2.5 inches. The resultingnarrow zone of protection is produced by the combination of theherbicide migrating directly into the soil from the uncoated sides ofthe layered nodules and from the exposed front surface of the carrierfrom the which herbicide is released over time.

The amount of herbicide released directly into the soil from theuncoated carrier sheet itself over time exceeds the amount released fromthe uncoated side of the carrier shown in the FIG. 22 embodiment. TheFIG. 23 embodiment combines this migration of the herbicide with thereduced release rate directly from the uncoated sides of the layeredsegments, caused by the barrier layers 126. This combined release ofherbicide narrows the zone of protection to the area most needed fortreatment. And it is believed that greater than about 50% of theherbicide is saved when compared to the prior art (as shown in FIGS. 1and 2) because of the reduced distance that the herbicide moves throughthe soil away from the fabric.

What is claimed is:
 1. A sheet material for preventing entry of unwantedroots into a volume of soil, comprising a flexible porous carrier sheetof a non-biodegradable polymeric herbicide-absorbing material; discretespaced-apart layered segments of a polymer containing a dinitroanilineherbicide positioned on a front surface of the carrier sheet, leaving anuncoated exposed surface of the carrier sheet in between thespaced-apart layered segments, the layered segments comprising acomposition effective to retain and control the release rate of saidherbicide; the layered segments having outer surface portions thereofcoated with a layer of barrier material that blocks diffusion of theherbicide directly from the portions of the layered segments that arecoated with the barrier material, for dispersing the herbicide at acombined controlled release rate directly away from any uncoated sidesof the layered segments and away from the uncoated exposed front surfaceof the carrier sheet.
 2. The sheet material according to claim 1 inwhich portions of the segments facing at least a back surface of thecarrier sheet are coated with the barrier material.
 3. The sheetmaterial according to claim 1 in which the layered segments aregenerally tapered and coated with the barrier material on a portionthereof that leaves said uncoated sides as exposed faces of the segmentsfacing generally more parallel to the carrier sheet.
 4. The sheetmaterial according to claim 1 in which a portion of the layered segmentslocated farthest from the front side of the carrier is coated with thebarrier material, leaving uncoated sides of the layered segments closerto the carrier sheet, from which the herbicide is released in adirection generally parallel to the front surface of the carrier,combined with the layers of barrier material on those portions of thesegments facing a back side of the carrier sheet.
 5. The sheet materialas defined in claim 1, in which the herbicide is absorbed in carbonblack, the concentration of the dinitroaniline herbicide in said layeredsegments being from about 2 wt. % to about 30 wt. %, based on the solidscontained in the layered segments, the carbon black effective to retainand control the release rate of the herbicide.
 6. The sheet material asdefined in claim 1, wherein said polymer contained in the layeredsegments is selected from the group consisting of polyethylenes,polypropylenes, copolymers and mixtures of polyethylenes andpolypropylenes, polyvinylacetate, poly(ethylene vinyl acetate),poly(ethylene acrylic acid), poly(ethylene ethyl acrylate),polybutylene.
 7. The sheet material as defined in claim 1, wherein saiddinitroaniline herbicide is selected from the group consisting oftrifluralin, benfluralin, isopropalin, oryzalin, ethalfluralin,pendimethalin, and profluralin.
 8. The sheet material as defined inclaim 1, wherein the carrier sheet material is selected from the groupconsisting of polyethylenes, polypropylenes, copolymers and mixtures ofpolyethylenes and polypropylenes, polyvinylacetate, poly(ethylene vinylacetate), poly(ethylene acrylic acid), poly(ethylene ethyl acrylate),polybutylene.
 9. The sheet material as defined in claim 1, wherein saidcarrier sheet is one of (a) to (c): (a) a fabric which is porous towater; (b) a non-woven fabric of a non-biodegradable thermoplasticpolyolefin material; or (c) a continuous non-porous sheet of anon-biodegradable polyolefin material.
 10. The sheet material as definedin claim 1, wherein said layered segments have a width greater thantheir thickness, in which the layered segments are from about ¼ to about1 inch in diameter and from about 1/40 inch to about ⅜ inch inthickness, and in which said layered segments are spaced apart by anaverage of about 1 to about 3 inches.
 11. The sheet material as definedin claim 1, in which the rate of diffusion of the herbicide from saidlayered segments into the carrier sheet material is controlled by adispersed nanoclay incorporated into the composition of said layeredsegments.
 12. The sheet material as defined in claim 1, in which thebarrier layer material comprises a paint film binder or lacquer selectedfrom the group consisting of EVOH, vinyl, polyolefin, polyurethane andacrylic.
 13. The material as defined in claim 1, wherein said carriersheet comprises a non-woven carrier sheet comprising a multilayerextrusion with at least one layer containing EVOH, or wherein saidcarrier sheet comprises a continuous non-porous polyolefin sheetcomprising a multilayer extrusion with at least one layer containingEVOH, or one layer containing a nanoclay, or one layer comprising apaint coat.
 14. The material as defined in claim 1, wherein said barriermaterial comprises a thin film or layer or coating of a polymericmaterial which optionally contains a dispersed nanoclay.
 15. Acombination of a zone of protection and a controlled release barrier,the zone of protection comprising a volume of soil from which unwantedroot growth is excluded; and a sheet material positioned in the soil forproviding a controlled release barrier that prevents entry of unwantedroots into the volume of soil, the sheet material comprising a flexibleporous carrier sheet of a non-biodegradable herbicide-absorbingthermoplastic polyolefin material; discrete spaced-apart layeredsegments of a polyolefin material containing a herbicidal dinitroanilinepositioned on a front surface of the carrier sheet, leaving an uncoatedexposed surface of the carrier sheet in between the spaced-apart layeredsegments, the layered segments comprising a composition effective toretain and control the release rate of said herbicide; the layeredsegments having outer surface portions thereof coated with a layer ofbarrier material that blocks diffusion of the herbicide directly intothe soil from the portions of the layered segments that are coated withthe barrier material, so that when said carrier sheet is buried in thevolume of soil, said herbicide is dispersed into the adjacent soildirectly away from the uncoated sides of the layered segments and awayfrom any uncoated exposed outer surface of the carrier sheet to formsaid zone of protection along the buried sheet material, the herbicidedispersed at such a release rate, and over such a period of time, as toexclude roots over a period of years without killing plants beyond theseedling stage.
 16. The combination according to claim 15 in whichportions of the segments facing at least a back surface of the carriersheet are coated with the barrier material.
 17. The combination definedin claim 15 in which the layered segments are generally tapered andcoated with the barrier material on a portion thereof that leaves saiduncoated sides as exposed faces of the segments facing generally moreparallel to the carrier sheet.
 18. The combination defined in claim 15,in which a portion of the layered segments located farthest from thefront side of the carrier is coated with the barrier material, leavinguncoated sides of the layered segments closer to the carrier sheet, fromwhich the herbicide is released in a direction generally parallel to thefront surface of the carrier, combined with the layers of barriermaterial on those portions of the segments facing a back side of thecarrier sheet.
 19. The combination defined in claim 15, wherein saidlayered segments are spaced apart disk-shaped elements, or continuous ordiscontinuous extrusions which have been applied to, bonded to, orembedded in the carrier sheet.
 20. The combination defined in claim 15,wherein said layered segments have a width greater than their thicknessand wherein the volume-to-area ratio of the layered segments is lessthan 0.10 inch.
 21. The combination defined in claim 15, in which ananoclay is incorporated into the composition of the layered segments,and in which a nanoclay is dispersed in either the barrier layermaterial, or the carrier sheet material, or both.
 22. The combinationdefined in claim 15, wherein said layered segments have a width greaterthan their thickness, in which the layered segments are from about ¼ toabout 1 inch in diameter and from about 1/40 inch to about ⅜ inch inthickness, and in which said layered segments are spaced apart by anaverage of about 1 to about 3 inches.
 23. The combination defined inclaim 15 in which the barrier layer material comprises a paint filmbinder or lacquer selected from the group consisting of EVOH, vinyl,polyolefin, polyurethane and acrylic.
 24. The combination defined inclaim 15, in which the zone of protection is located in a septicdrain-field or a waste burial site.
 25. A method for creating a narrowherbicidal zone of protection in a volume of soil to protect againstunwanted root growth in the zone of protection, the method comprising:positioning a herbicidal root growth barrier in the soil; the rootgrowth barrier comprising a sheet material for preventing entry ofunwanted roots into the volume of soil, comprising a flexible porouscarrier sheet of a non-biodegradable polymeric herbicide-absorbingmaterial; discrete spaced-apart layered segments of a polymer containinga dinitroaniline herbicide positioned on a front surface of the carriersheet, leaving an uncoated exposed surface of the carrier sheet inbetween the spaced-apart layered segments, the layered segmentscomprising a composition effective to retain and control the releaserate of said herbicide; the layered segments at least having portions oftheir outer surfaces coated with a layer of barrier material to blockdiffusion of the herbicide directly through said barrier material intothe soil; the barrier layers causing the herbicide contained in thelayered segments to be dispersed away from any uncoated sides of thelayered segments and into the soil and from the layered segmentslaterally through the herbicide-absorbing carrier sheet, for ultimatelydispersing the herbicide into the soil at a combined release rate tothereby form said narrow zone of protection along the buried sheetmaterial.
 26. The method defined in claim 25, wherein said carrier sheetis one of (a) to (c): (a) a fabric which is porous to water; (b) anon-woven fabric of a non-biodegradable thermoplastic polyolefinmaterial; or (c) a continuous non-porous sheet of a non-biodegradablepolyolefin material.
 27. The method of claim 25, in which the layeredsegments are generally tapered and coated with the barrier material on aportion thereof that leaves said uncoated sides as exposed faces of thesegments facing generally more parallel to the carrier sheet.
 28. Themethod of claim 25 in which a portion of the layered segments locatedfarthest from the front side of the carrier is coated with the barriermaterial, leaving uncoated sides of the layered segments closer to thecarrier sheet, from which the herbicide is released in a directiongenerally parallel to the front surface of the carrier, combined withthe layers of barrier material on those portions of the segments facinga back side of the carrier sheet.
 29. The method of claim 25 in whichportions of the segments facing at least a back surface of the carriersheet are coated with the barrier material.
 30. A sheet material forpreventing entry of unwanted roots into a volume of soil, comprising aflexible carrier sheet of a non-biodegradable polymericherbicide-absorbing material; discrete spaced-apart layered segments ofa polymer containing a dinitroaniline herbicide positioned on an outersurface of the carrier sheet, leaving an uncoated exposed surface of thecarrier sheet in between the spaced-apart layered segments, the layeredsegments comprising a composition effective to retain and control therelease rate of said herbicide; the layered segments having outersurfaces coated with a layer of barrier material so that the layeredsegments block diffusion of the herbicide directly through said barriermaterial, to cause essentially all of the herbicide contained in thelayered segments to be dispersed away from the layered segments andlaterally through the herbicide-absorbing carrier sheet, for ultimatelydispersing the herbicide away from the uncoated exposed outer surface ofthe carrier sheet and into the soil at a controlled release rate.